For example, in large-scale backbone networks of telecommunication carriers, optical networks (NW) to which the wavelength division multiplexing (WDM) technology is applied have been built. The WDM technology is a technology to accommodate a plurality of user traffics in optical signals of different wavelengths among nodes connected with optical fibers, and to multiplex the plurality of optical signals into one optical fiber and transfer the signals in large capacity.
As an example of a technical standard of the optical NW, there is an optical transport network (OTN). The OTN includes two types of paths including an electric layer path and a wavelength path. The electric layer path is a path set between bases where users perform communication in an end-to-end manner, and which accommodates traffic. Further, the wavelength path is a path set between nodes where WDM transfer is executed, and obtained such that a plurality of electric layer paths is multiplexed and mapped into optical signals of different wavelengths. The OTN builds a high-speed and flexible optical NW, using these two types of paths.
However, in recent years, expectation to introduce software defined networking (SDN) has been increasing, which realizes management and control of the NW with software. The optical NW is also demanded to support the SDN to enable store flexible and dynamic control.
In the SDN, a use request from a user or various applications to the optical NW, that is, a request of demand, becomes easy. Therefore, a demand of traffic, for example, the number of wavelength links used between the nodes is dynamically changed according to a time zone. For example, the traffic of the optical NW largely varies by a rapid increase in the demand such as distribution of popular content, and the like.
FIGS. 17A to 17D are explanatory diagrams illustrating an example of a path configuration of an optical transfer system. The optical transfer system illustrated in FIGS. 17A to 17D builds the optical NW that connects five nodes including the first to fifth nodes 100A to 100E with an optical fiber 101. The first node 100A is connected with the second node 100B, using the optical fiber 101 of a first section 101A, and is connected with the fifth node 100E, using the optical fiber 101 of a fifth section 101E. The second node 100B is connected with the third node 100C, using the optical fiber 101 of a second section 101B, and is connected with the fifth node 100E, using the optical fiber 101 of a sixth section 101F. The third node 100C is connected with the fourth node 100D, using the optical fiber 101 of a third section 101C. The fourth node 100D is connected with the fifth node 100E, using the optical fiber 101 of a fourth section 101D.
The optical NW in a time zone t1 accommodates, as illustrated in FIG. 17A, a demand D101 in the first section 101A, a demand D102 in the sixth section 101F, and a demand D103 in the third section 101C.
Next, as illustrated in FIG. 17B, assume that, in the optical NW in a time zone t2, a demand D104 from the first node 100A to the third node 100C has newly occurred, and a demand D105 from the fourth node 100D to the fifth node 100E has newly occurred. The optical NW accommodates the demand D104 in the first section 101A and the second section 101B, and accommodates the demand D105 in the fourth section 101D. As a result, a traffic amount in the first section 101A is further increased as well as that in the fourth section 101D, compared with those in the time zone t1.
Further, as illustrated in FIG. 17C, assume that, in the optical NW in a time zone t3, a demand D106 from the first node 100A to the third node 100C has newly occurred, and a demand D107 from the first node 100A to the fifth node 100E has newly occurred. The optical NW accommodates the demand D106 in the first section 101A and the second section 101B, and accommodates the demand D107 in the fifth section 101E. As a result, the traffic amounts of the first section 101A and the second section 101B are further increased, compared with those in the time zone t2.
Further, as illustrated in FIG. 17D, assume that, in the optical NW in a time zone t4, a demand D108 from the first node 100A to the second node 100B has newly occurred. The optical NW accommodates the demand D108 in the first section 101A. As a result, the traffic amount of the first section 101A is further increased, compared with that in the time zone t3. Therefore, the traffic amounts of the respective sections largely vary according to the increase in the demand.
Therefore, to absorb the varying traffic demand, for example, there is a method of making an upper limit number of all of wavelength links in the nodes active. However, many lasers constantly need to be active, and thus the power consumption is large. Furthermore, when the actual traffic has been decreased than expected, sections with excessive wavelength links occur, and communication efficiency to operation cost is decreased.
Therefore, the optical NW is desired to efficiently use the wavelength resource by dynamically performing addition/deletion of the wavelength links according to an actual use state.
Therefore, for example, as a technology to dynamically perform addition of the wavelength link, a technology to measure a traffic amount transferred in each node, and generate an optical bypass link when congestion is caused in the optical link to detour a part of the traffic is known.
However, when the wavelength link is dynamically added according to the actual use state, the laser needs to be set active every time the wavelength link is added, and it takes a time until the added wavelength link is operated. To secure a stable output of the laser, adjustment of a device temperature and the like takes several, minutes to several tens of minutes of time. Therefore, it takes a time from an instruction of addition of the wavelength link to start of the operation of the wavelength link. Therefore, it is difficult for a route for accommodating the demand to be secured, and a call loss may occur. Therefore, a free bypass route that needs a higher route cost than an optimum route is searched for, and the demand is accommodated in the bypass route, and thus occurrence of the call loss can be suppressed.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2013-168732
Patent Literature 2: Japanese Laid-open Patent Publication No. 2013-70200
Patent Literature 3: International Publication Pamphlet No. WO 2009/025329
Patent Literature 4: Japanese National Publication of International Patent Application No. 2012-502584
In the optical NW, when the section on the optimum route to the demand is insufficient, the bypass route that needs a higher route cost than the optimum route is determined, and the demand is accommodated in the determined bypass route. However, normally, when a new demand has occurred where the bypass route is used as the optimum route, it is difficult for the optimum route to the demand to be secured, and the demand is accommodated in a further bypass route. As a result, a vicious circle that incurs further bandwidth consumption of the route is caused, and the use efficiency of the wavelength resource is decreased.
Further, when a demand from the first node 100A to the third node 100C occurs, the optimum route becomes the first section 101A and the second section 101B. For convenience of description, the route cost between the nodes 100 is calculated by the number of single hops. However, when the first section 101A has an insufficient bandwidth, bypass routes of the fifth section 101E, the fourth section 101D, and the third section 101C are determined. Then, the demand from the first node 100A to the third node 100C is accommodated in the bypass routes of the fifth section 101E, the fourth section 101D, and the third section 101C.
However, normally, the wavelength links of the first section 101A and the second section 101B are enough to accommodate the demand. However, due to insufficiency of the bandwidth of the first section 101A, the bypass routes of the third section 101C, the fourth section 101D, and the fifth section 101E are used. Further, when a new demand, that uses the fourth section 101D as the optimum route occurs, and when the fourth section 101D has already been used as the bypass route of another demand, and has an insufficient bandwidth, a bypass route is searched for the new demand, and the demand is accommodated in the bypass route. That is, if the bandwidth, consumption is increased due to the bypass route, it is difficult for the demand occurring afterward to be accommodated in the optimum route and the demand is highly possibly accommodated in the bypass route, and the vicious circle that incurs further bandwidth consumption is caused and the use efficiency of the wavelength resource is decreased.